N-face GaN MOCVD Growth on Misoriented Substrates
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Solution Overview
Problem
The growth of high-quality N-polar group III nitride films and heterostructures is challenging due to difficulties in achieving smooth surfaces and high In composition in InGaN, as well as low resistance p-type (Al,Ga,In)N:Mg films, which limits the types of devices that can be fabricated, particularly for LEDs and transistors.
Innovation Solution
A method for heteroepitaxial growth of N-face GaN, InN, and AlN, and their alloys using Metal Organic Chemical Vapor Deposition (MOCVD) on misoriented substrates, which includes forming an AlN layer to set N-polarity and growing the nitride layers with specific misorientation angles and doping techniques to achieve smoother films and improved doping profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Ga-polar group III nitride films are used for device fabrication, then the growth process is well-established and devices can be fabricated, but the piezoelectric field direction limits the types of devices that can be made and reduces carrier injection efficiency
Solution Approach 1:
The patent inverts the conventional growth approach by growing N-polar group III nitride films instead of the traditional Ga-polar films. This inversion changes the direction of piezoelectric fields in the heterostructure, enabling fabrication of transistor devices and improving carrier injection efficiency that cannot be achieved with Ga-polar films.
2Reliability
If N-polar group III nitride films are grown to improve device performance, then carrier injection and piezoelectric field direction are improved, but surface smoothness and film quality deteriorate
Solution Approach 1:
The patent applies local quality by creating a graded buffer layer structure where the composition and properties vary locally through the layer stack. This allows the bottom layers to provide structural support and the upper layers to provide smooth surfaces for device fabrication, resolving the contradiction between bulk properties and surface quality.
Solution Approach 2:
The patent changes growth parameters including temperature, pressure, and precursor ratios during the MOCVD process to optimize both film quality and surface smoothness. By dynamically adjusting these parameters, the process achieves high-quality N-polar films with acceptable surface morphology for device fabrication.
3Adaptability or versatility
If high indium content InGaN is grown to broaden spectral applications, then the spectral range is expanded, but surface roughness increases and film quality deteriorates
Solution Approach 1:
The patent uses local quality by implementing graded buffer layers with gradually varying indium content. This allows high indium content regions to provide broad spectral emission while the lower indium content regions maintain structural integrity and surface smoothness, enabling high-quality films with expanded spectral applications.
4Quantity of substance
If p-type (Al,Ga,In)N:Mg films are grown to improve hole injection, then carrier concentration is increased, but polarity conversion from Ga-face to N-face occurs at high doping levels
Solution Approach 1:
The patent inverts the conventional approach by growing N-polar films instead of Ga-polar films. This inversion stabilizes the polarity at high magnesium doping levels, preventing the polarity conversion that normally occurs in Ga-polar films and enabling high carrier concentration with maintained structural stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the growth of high-quality N-face nitride films with improved carrier injection and lower operating voltages, allowing for the fabrication of more efficient LEDs, transistors, and other nitride-based devices with enhanced performance, including higher indium content InGaN alloys for broader spectral applications.
Implementation Method 1
A method for heteroepitaxial growth of N-face GaN, InN, and AlN, and their alloys using Metal Organic Chemical Vapor Deposition (MOCVD)
Implementation Method 2
forming an AlN layer to set N-polarity and growing the nitride layers with specific misorientation angles
Data Source
AI summary
Methods for the heteroepitaxial growth of smooth, high quality films of N-face GaN film grown by MOCVD are disclosed. Use of a misoriented substrate and possibly nitridizing the substrate allow for the growth of smooth N-face GaN and other Group III nitride films as disclosed herein. The present invention also avoids the typical large (μm sized) hexagonal features which make N-face GaN material unacceptable for device applications. The present invention allows for the growth of smooth, high quality films which makes the development of N-face devices possible.